1. Field of the Invention
The present invention relates to door locks, and in particular to electric door locks that can be operated in both the fail-safe and fail-secure mode.
2. Description of the Related Art
Security doors to prevent theft or vandalism have evolved over the years from simple doors with heavy duty locks to more sophisticated egress and access control devices. Hardware and systems for limiting and controlling egress and access through doors are generally utilized for theft-prevention or to establish a secured area into which (or from which) entry is limited. For example, retail stores use such secured doors in certain departments (such as, for example, the automotive department) which may not always be manned to prevent thieves from escaping through the door with valuable merchandise. In addition, industrial companies also use such secured exit doors to prevent pilferage of valuable equipment and merchandise.
One type of door lock which has been used in the past to control egress and access through a door is an electromagnetic system which utilizes an electromagnet mounted on a door jamb, with an armature mounted on the door held by the electromagnet to retain the door in the closed position when the electromagnet is actuated. Such locking mechanisms are illustrated in U.S. Pat. No. 4,439,808, to Gillham, U.S. Pat. No. 4,609,910, to Geringer et al., U.S. Pat. No. 4,652,028, to Logan et al., U.S. Pat. No. 4,720,128 to Logan, Jr., et al., and U.S. Pat. No. 5,000,497, to Geringer et al. All of these references utilize an electromagnet mounted in or on a door jamb and an armature on the door held by the electromagnet to retain the door in the closed position. Such electromagnetic locking systems are quite effective at controlling egress and access through the door they are installed on. Unfortunately, however, such systems are quite expensive, and require a fairly complex installation, often with the electromagnet being mounted in the door jamb.
Another type of system which is known in the art is the electric door strike release mechanism, in which a latch bolt located in and extending from a locking mechanism located in a door is receivable in an electrically operable door strike mounted in the frame of the door. The door may be opened either by retracting the latch bolt into the locking mechanism to thereby disengage it from the door strike, or by electrically actuating the door strike mechanism to cause it to open and to thereby release the extended latch bolt from the door strike mechanism. Typically, such electrically operable door strikes pivot to allow the door to close without the door strike mechanism being electrically actuated. Such door strike mechanisms are illustrated in U.S. Pat. No. 4,017,107, to Hanchett, U.S. Pat. No. 4,626,010, to Hanchett et al., and in U.S. Pat. No. 5,484,180, to Helmar. Like the electromagnet/armature systems discussed above, electrically operated door strike systems are also expensive, and require a significant installation into the door jamb, which must usually be reinforced.
Electrically operable door locks have also been developed that can be installed on a door through which access is to be controlled by an electrically operable security system. Such a lock is disclosed in U.S. Pat. No. 5,876,073 to Geringer et al. The door opening mechanism of the door lock is selectively locked and unlocked by controlling the supply of electricity to the door lock to thereby control access or egress through the door. The electrically operable door lock uses an electromagnetic actuator to drive a locking member between a locked position in which it engages a latch actuating member to prevent it from being rotated to retract a latch bolt to open a door, and an unlocked position in which it is disengaged from the latch actuating member to allow it to be rotated to retract the latch bolt to open the door. By reversing the position of the electromagnetic actuator in the door lock apparatus, the system may operate in either a fail secure mode in which the electromagnetic actuator must be powered to unlock the door, or a fail safe mode in which the electromagnetic actuator must be powered to lock the door.